As sections of railroad are constructed it is necessary to weld one rail to the adjacent rail. The rails are welded end-to-end by a process called thermetic welding. In this process, the rails are placed in the desired positions. A material designed to burn at high temperature is wrapped around the rail joint and ignited. It burns at a high temperature and welds the rails together their entire cross-section.
This process sometimes creates bubbles or other flaws that lead to a weakening of the joint. It is necessary to identify these flaws so that the joint be replaced with a stronger joint without weld flaws.
Rails and weld also deteriorate with time and use. Therefore there is also a need to inspect rails and welds for flaws created by extended service & fatigue.
Since there is a large amount of weight carried by the rails, flaws may cause weakened sections and result in a derailment.
There are ultrasonic inspection devices to inspect welds in specific geometries such as sheets and plates, such as U.S. Pat. No. 3,552,191 Jan. 5, 1971 by Heseding. This uses multiple ultrasound (US) transmitters that are also US receivers on one side of a weld on a sheet or plate. They also have embodiments that transmit across the weld to be received by a receiver on the other side of the weld. This apparatus is designed to inspect welds in flat plates and does not function well to inspect objects with substantially different geometry such as railroad rails.
U.S. Pat. No. 3,028,751 issued Apr. 10, 1962 to I. L. Joy describes a device designed to quickly detect locations that may possibly have flaws. It does not perform a thorough scan through the rail, but a more cursory scan to detect a general region have a large flaw.
Currently, there is a need for an inspection device that more accurately identifies flaws in railroad rail thermite welds.